The present invention relates to an apparatus and method for forming threads in a tube.
There are tubes employed in various applications where the tubes require a very limited number of relatively course (partial) threads on one end. For example, a fuel filler tube that extends from a vehicle fuel tank to an opening in the side of the vehicle will have threads at one end for securing a mating part thereto. It may be desirable for the mating part to only need, for example, one quarter or one half turn to be fully engaged with the tube. The threads, then, may each extend only part of the way around the circumference of the tube. In such tubes, a metal forming operation is employed to form these partial threads rather than cutting threads into the tube, as may be the case with tubes that have a full set of threads on their ends.
In the past, such tubes with these partial threads may have been roll formed, or have the threads formed in a six-segment die actuated by a large press. But these processes have drawbacks, including, for example, a limited ability to adapt to changes in tube outside diameters, and a limited ability to detect an out of tolerance part before or during the thread forming process. Still other forming processes mate one side of the tube with a die and apply pressure via a second die being pressed from the opposite side. But such asymmetrical processes do not always produce the desired result. Since these partial threads are not necessarily formed all of the way around the tube, there is not equal pressure all of the way around, so the tube may tend to deform to an oval shape at the location of the threads.
Thus, it is desirable to form partial threads on a tube while overcoming the drawbacks of the prior art.